dhcp ipv6 unexpected subnetmask /128

Wed May 2 13:11:09 UTC 2012

Hi ,

I am not exactly sure of this.
But as far as i know, prefix length is managed by router advertisements
i.e., RA .

If you use prefix delegation there is a provision for sending prefix length
i think.

Please refer to the link

http://docs.oracle.com/cd/E19082-01/819-3000/geflo/index.html

* *

*Differences between DHCPv4 and DHCPv6*

The two major differences between DHCPv4 and DHCPv6 are the following:

·         *The administrative model*

o    DHCPv4–The administrator enables DHCP for each interface.
Administration is on a per-logical interface basis.

o    DHCPv6–Explicit configuration is not necessary. This protocol is
enabled on a given physical interface.

·         *Protocol details*

o    DHCPv4–The DHCP server supplies the subnet mask for each address. A
hostname option sets the system-wide node name.

o    DHCPv6–The subnet mask is supplied by Router Advertisements, not the
DHCPv6 server. There is no DHCPv6 hostname option.

It clearly mentions that DHCPv6 doesn’t handle subnet mask (prefix length)
management.

http://tools.ietf.org/html/rfc4861#section-4.2

Also refer this.

In router advertisement ,M bit should be set for DHCPv6.

4.2 <http://tools.ietf.org/html/rfc4861#section-4.2>.  Router Advertisement
Message Format

   Routers send out Router Advertisement messages periodically, or in

   response to Router Solicitations.

      0                   1                   2                   3

      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |     Type      |     Code      |          Checksum             |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     | Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                         Reachable Time                        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |                          Retrans Timer                        |

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     |   Options ...

     +-+-+-+-+-+-+-+-+-+-+-+-

   IP Fields:

      Source Address

                     MUST be the link-local address assigned to the

                     interface from which this message is sent.

Narten, et al.              Standards Track                    [Page 19]

  <http://tools.ietf.org/html/rfc4861#page-20>

RFC 4861 <http://tools.ietf.org/html/rfc4861>               Neighbor
Discovery in IPv6         September 2007

      Destination Address

                     Typically the Source Address of an invoking Router

                     Solicitation or the all-nodes multicast address.

      Hop Limit      255

   ICMP Fields:

      Type           134

      Code           0

      Checksum       The ICMP checksum.  See [ICMPv6
<http://tools.ietf.org/html/rfc4861#ref-ICMPv6>].

      Cur Hop Limit  8-bit unsigned integer.  The default value that

                     should be placed in the Hop Count field of the IP

                     header for outgoing IP packets.  A value of zero

                     means unspecified (by this router).

      M              1-bit "Managed address configuration" flag.  When

                     set, it indicates that addresses are available via

                     Dynamic Host Configuration Protocol [DHCPv6
<http://tools.ietf.org/html/rfc4861#ref-DHCPv6>].

                     If the M flag is set, the O flag is redundant and

                     can be ignored because DHCPv6 will return all

                     available configuration information.

      O              1-bit "Other configuration" flag.  When set, it

                     indicates that other configuration information is

                     available via DHCPv6.  Examples of such information

                     are DNS-related information or information on other

                     servers within the network.

On Wed, May 2, 2012 at 6:03 PM, MAYER Hans <mayer at iiasa.ac.at> wrote:

>
> Dear all
>
> I am running DHCP Server 4.1-ESV-R4 on a Solaris 11 machine. In the same
> network also a Windows 7 client is connected, all within GNS3.
>
> This is my simple configuration: ( maybe too simple )
>  /etc/inet/dhcpd6.conf
>
> # dhcpd.conf
> # Sample configuration file for ISC dhcpd
> default-lease-time 600;
> max-lease-time 7200;
> allow leasequery;
> log-facility local7;
> shared-network LAN {
>  subnet6 2001:628:21f0:1::/64 {
>        range6 2001:628:21f0:1::100 2001:628:21f0:1::1ff ;
>        option dhcp6.name-servers 2001:628:21f0:1::1 ;
>        option dhcp6.domain-search "iiasa.ac.at" ;
>  }
> }
>
>
> Within Solaris I have the following fixed IP configured:
> e1000g1:3: flags=20002000941<UP,RUNNING,PROMISC,MULTICAST,IPv6> mtu 1500
> index 9
>        inet6 2001:628:21f0:1::1/64
>
> I start the dhcpd with the following command in the foreground:
> /usr/lib/inet/dhcpd -6  -d -cf /etc/inet/dhcpd6.conf -lf
> /var/db/isc-dhcp/dhcpd6.leases
>
> After a while I see on Solaris 11 the following interface:
> e1000g1:2: flags=20002004941<UP,RUNNING,PROMISC,MULTICAST,DHCP,IPv6> mtu
> 1500 index 9
>        inet6 2001:628:21f0:1::160/128
>
> To check on Windwos I do: netsh interface ipv6 show  route
> And I see:
> No       Manual    256  2001:628:21f0:1::1ba/128   15  Local Area
> Connection 2
>
> In both cases a /128 subnet mask.
> Why /128 ?
>
> I can ping the link-local address of the other site in each case but I
> cannot ping the official 2001:... address. I can ping the own IPv6 address
> but not the other as it is /128 and therefore not accessible within the
> network. I would expect that the dhcp daemon gives a /64 address as defined
> in the 'subnet6' declaration.
>
> Some ideas what I did wrong ?
>
> Kind regards
> Hans
>
>
> --
>
>
>
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> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
>

-- 
Regards,
Mukund
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